Impurity-induced layer disordering (IILD) or layer intermixing is a well studied phenomena in the III-arsenide and III-phosphide material systems, but has not been conclusively identified in Ill-nitride materials. See W. D. Laidig et al., Appl. Phys. Lett. 38, 776 (1981); D. G. Deppe and N. Holonyak, Jr., J. Appl. Phys. 64, R93 (1988); and D. G. Deppe et al., Appl. Phys. Lett. 52, 1413 (1988). Normally an unintentionally doped (UID) heterointerface such as an AlAs/GaAs is stable (no Al—Ga interdiffusion) up to high temperatures (˜900° C.). See L. L. Chang and A. Koma, Appl. Phys. Lett. 29, 138 (1976). The introduction of impurities by diffusion, implantation, or during growth lowers the temperature where layer disordering can occur (˜500° C. for Zn in III-As). See W. D. Laidig et al., Appl. Phys. Lett. 38, 776 (1981). Beyond the obvious materials science interests, layer disordering has many practical uses in device fabrication by using selective layer disordering for carrier and photon confinement. See K. Meehan et al., Appl. Phys. Lett. 44, 428 (1984).
III-nitrides are believed to be stable under standard growth and processing temperatures, because of the high crystal bond strength and low diffusivity of impurities. Layer intermixing in GaN/AlGaN heterostructures with no impurities is observed at temperatures of ˜1500° C. See S. Porowski et al., J. Phys., Condens. Matter. 14, 11097 (2002). Other reports of layer disordering of III-nitrides claim only localized intermixing in AlGaN/GaN observed at line defects, or with InGaN/GaN heterostructures at temperatures much higher than the InGaN growth temperature making it unclear if an impurity-induced layer disordering process is occurring. See A. Y. Polyakov et al., J. Elec. Mat. 31, 384 (2002); M. D. McCluskey et al., MRS Internet J. Nitride Semicond. Res. 4S1, G3.42 (1999); and M. C. Y. Chan et al., MRS Internet J. Nitride Semicond. Res. 4S1, G6.25 (1999).
There is continued interest in using the large conduction band offsets (˜2 eV) of AlGaN-based heterostructures to create superlattice (SL) structures with near-infrared intersubband energy transitions for devices such as optical switches and detectors. See N. Iizuka et al., Optics Express 13, 3835 (2005); and D. Hofstetter et al., Appl. Phys. Lett. 83, 572 (2003). Typically these heavily doped AlGaN heterostructures are grown by molecular beam epitaxy (MBE) to achieve the abrupt interfaces in thin (<50 Å) well layers required to achieve short wavelength and narrow intersubband energy transitions. See C. Gmachl et al., Appl. Phys. Lett. 77, 334 (2000). Recently, progress has been made to improve heterointerface abruptness in metal-organic vapor phase epitaxy (MOVPE) grown III-nitride intersubband. Nicoly et al. claims reduced layer roughness in GaN/Al(In)N SLs by altering the interface surface during growth using indium as a surfactant. See S. Nicolay et al., Appl. Phys. Lett. 88, 151902 (2006). Yang et al. states layer interdiffusion is caused simply by higher growth temperatures and suggests a possible role of gas phase reactions while not identifying high Si doping and thus IILD as a possibility. See J.-S. Yang et al., Appl. Phys. Lett. 95, 162111 (2009).
However, a need remains for a method of layer intermixing in the III-nitride material systems.